1. Field of the Invention
This invention, relates to a non-resonant monopole antenna having a ground plane. More particularly, this invention relates to a monopole antenna which has a relatively short length and provides a broad band antenna with an effective length of an infinitely long antenna.
2. Description of the Prior Art
Monopole antennas having associated ground planes are known. Such monopole antennas are also known to have a relatively narrow bandwidth which is caused by reflections of the signals being applied to the antenna.
Dipole antennas which do not have associated ground planes are well known. Such dipole antennas are also known to have a relatively narrow bandwidth which is also caused by reflections of the signals being applied to the relatively short length of antenna.
Motohisa Kanda disclosed a broad band antenna in "IEEE Transactions on Antennas and Propagation", Vol. AP-26, No. 3, May, 1978 at pages 439 to 447. The antenna disclosed in this article comprised a nonconducting cylinder on which had been deposited a varying-conductivity resistive film. To achieve a flat frequency response curve, it was necessary to calculate the thickness of the film along the length of the cylinder using the "method of moments" approach. The resulting thin film antenna requires a complex calculation and deposition, yet does not always achieve the desired response.
Motohisa Kanda also disclosed a broad band antenna in the magazine "Microwaves", January, 1981 issue, at pages 63 to 66. The dipole antenna disclosed in this article was resistively loaded and also comprised a thin film of resistive alloy deposited on a glass rod. The thickness of the thin film necessary to achieve a desired bandwidth was also calculated by the "method of moments" approach.
While resistively loaded antennas will provide a broad band antenna, such antennas are difficult to make and there is no provision for making any final adjustment to imperfections in the response curves. Further, such resistive film antennas do not provide any means for selectively eliminating frequencies within the broad band being propagated.
It would be extremely desirable to provide a relatively short monopole antenna which has a substantially flat response curve and which can be adjusted for imperfections in the response curve to enhance or eliminate predetermined frequencies within the broad band of frequencies and to provide a broad band antenna which has an infinite effective length over a broad band of frequencies.